This article explains a surprising wave of lethal attacks by drug cartels against hundreds of local elected officials and party candidates in Mexico, 2007–2012. These attacks are puzzling because criminal organizations tend to prefer the secrecy of bribery over the publicity of political murder. Scholars suggest that war drives armed actors to attack state authorities in search of protection or rents. Using original data on high-profile attacks in Mexico, the authors show that war need arguments underexplain violence. Focusing on political opportunities, they suggest that cartels use attacks to establish criminal governance regimes and conquer local governments, populations and territories. The study presents quantitative and qualitative evidence showing that cartels took advantage of Mexico's political polarization and targeted subnational authorities who were unprotected by their federal partisan rivals. Cartels intensified attacks during subnational election cycles to capture incoming governments and targeted geographically adjacent municipalities to establish control over large territories. The findings reveal how cartels take cues from the political environment to develop their own de facto political domains through high-profile violence. These results question the widely shared assumption that organized criminal groups are apolitical actors.